Method for preparation of metal intercalated fullerene-like metal chalcogenides

ABSTRACT

A method for the preparation of nanoparticles of metal oxides containing inserted metal particles and to metal-intercalated and/or metal-encaged “inorganic fullerene-like” (hereinafter IF) structures of metal chalcogenides obtained therefrom is provided, which comprises heating a metal I material with water vapor or electron beam evaporation of said metal I material with water or another suitable solvent, in the presence of a metal II salt, and recovering the metal II-doped metal I oxide, or proceeding to subsequent sulfidization, yielding bulk quantities of metal II-intercalated or metal II-encaged IF structures of the metal I chalcogenide. The metal II salt is preferably an alkaline, alkaline earth or transition metal salt, most preferably an alkali chloride. The intercalated and/or encaged IF structures are usable as lubricants. They also form stable suspensions, e.g. in alcohol, and electrophoretic deposition from said suspensions yields thin films of the intercalated IF materials, which have a range of potential applications.

CROSS REFERENCE TO RELATED APPLICATION

The present application is the national stage under 35 U.S.C. 371 ofPCT/IL97/00390, filed Nov. 27, 1997.

FIELD OF THE INVENTION

The present invention relates to a method for the preparation ofnanoparticles of metal oxides containing inserted metal particles and tometal-intercalated and/or metal-encaged “inorganic fullerene-like”(hereinafter IF) structures of metal chalcogenides obtained therefrom.According to the invention, either heating a metal I material with watervapor or electron beam evaporation of said metal I material with wateror another suitable solvent, in the presence of a metal II salt,produces metal II-doped metal I oxides, and subsequent sulfidization,yields bulk quantities of metal II-intercalated or metal II-encaged IFstructures (nested fullerenes, nanotubes, and structures with negativecurvature) of metal I chalcogenides. The intercalated and/or encaged IFstructures form stable suspensions, e.g. in alcohol, and electrophoreticdeposition from said suspensions yields thin films of the intercalatedIF materials, with a range of potential applications such as thephotosensitive element in solar cells, for the fabrication of inertscanning probe microscope (SPM, that includes both STM=scanningtunneling microscope and SFM=scanning force microscope) tips, secondarybatteries and electrochromic devices. The metal-intercalated ormetal-encaged IF structures can further be used as solid lubricants.

BACKGROUND OF THE INVENTION

Nanoclusters of various inorganic layered compounds, like metaldichalcogenides—MX₂ (M=Mo,W;X=S,Se), are known to be unstable in theplanar form and to form a hollow cage—inorganic fullerene-like (IF—MX₂)structures such as nested fillerenes and nanotubes (Tenne et al., 1992;Feldman et al., 1995 and 1996; published European Patent application No.EP 0580019) and structures with negative curvature (Schwartzites). Notsurprisingly, nanoparticles of hexagonal boronitrides with graphite-likestructure behaved similarly (Stephan et al., 1994; Chopra et al., 1995).Furthermore, nested fullerene-like polyhedra of MoS₂ were synthesized atroom temperature by a stimulus from an electron beam (José-Yacamán etal., 1996) in analogy to carbon-nested fullerenes (Ugarte, 1992), andalso by application of an electric pulse from the tip of a scanningtunneling microscope (STM) (Homyonfer et al., 1996).

Intercalation of carbon nanotubes with alkali metal atoms from the vaporphase was recently described (Zhou et al., 1994). The intercalated filmswere found to arrange in stage-1 (n=1) superlattice, i.e. alkali-metallayers were stacked between each two carbon layers. The compositenanostructures were found to disintegrate when exposed to air, andcomplete shattering of the nanotubes (exfoliation) was obtained uponimmersion in water. The intercalation of 2 H—MoS₂ and 2 H—WS₂ compoundswas discussed in detail (Brec and Rouxel, 1986; Friend and Yoffe, 1987;Somoano et al., 1973), but staging was not observed in either of theformer compounds, i.e. the alkali atoms were found to have a randomdistribution. Here too, deintercalation occurs upon exposure to air andexfoliation upon immersion in water.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a new method for thesynthesis of large quantities of IF structures of metal chalcogenidesthat affords intercalation of the IF structures with various metalatoms. Metal intercalation has a remarkable influence on the solubilityof these IF structures in aprotic solvents. The formations of stablesuspensions from the metal-intercalated or metal-encaged IF structurespermits deposition of thin films, with a range of potential applicationssuch as the use of such films as the photosensitive element in solarcells, for the fabrication of inert SPM tips, secondary batteries andelectrochromic devices.

The present invention thus relates, in one aspect, to a method for thepreparation of nanoparticles or nanowhiskers of a metal II-doped metal Ioxide, wherein said metal I is selected from In, Ga, Sn and a transitionmetal and said metal II is any metal, preferably a metal selected froman alkali, alkaline earth or a transition metal, which method comprises:

(i) heating a metal I material with water in a vacuum apparatus at abase pressure of 10⁻³ to 10⁻⁵ Torr or electron beam evaporating a metalI material with water or with an oxygen-containing volatile solvent in avacuum apparatus at a base pressure of 10⁻⁵ to 10⁻⁶ Torr, in thepresence of a metal II salt, and

(ii) recovering the metal II-doped metal I oxide from the walls of thevacuum apparatus.

The metal I material may be the metal I itself or a mixture of 2 or moredifferent metals I, or a substance comprising a metal I or a mixture ofsubstances comprising 2 or more different metals I. Examples oftransition metals include, but are not limited to, Mo, W, V, Zr, Hf, Pt,Re, Nb, Ta Ti, and Ru. The elctron beam evaporation embodiment is moresuitable for refractory transition metals, e.g. Nb, V, Ta, Ti.

Examples of metal II salts include, but are not limited to, alkali metalchlorides such as NaCl, KCl, LiCl and CsCl. Examples of doped oxidesthus prepared include, but are not limited to, Na, K, Li or Cs-dopedMoO_(3−x), preferably MoO₂ and MoO_(3,), or Na, K, Li or Cs-dopedWO_(3−x), preferably WO₃ and W₁₈O₄₉, or Na, K, Li or Cs-doped mixedoxide such as Mo_(x)W_(1−x)O₃, wherein x is from 0 to 1, and Na, K, Lior Cs-doped V₂O₅, preferably Li-doped V₂O₅.

According to the invention, the metal II salt may be added to the wateror to the oxygen-containing volatile solvent, or when it is NaCl or KCl,it is already present in the water.

Examples of suitable oxygen-containing volatile solvents are, withoutbeing limited to, acetone, ethanol, methanol.

The metal II-doped metal I oxides thus prepared are useful as startingproducts for the preparation of metal II-intercalated and/or metalII-encaged inorganic fuillerene-like (IF) structures of a metal Ichalcogenide, wherein metal I and metal II are as defined above, whichmethod comprises:

(i) heating a metal I material with water in a vacuum apparatus at abase pressure of 10⁻³ to 10⁻⁵ Torr or electron beam evaporating a metalI material with water or with an oxygen-containing volatile solvent in avacuum apparatus at a base pressure of 10⁻⁵ to 10⁻⁶ Torr, in thepresence of a metal II salt;

(ii) arnealing the metal II-doped metal I oxide obtained in step (i) ina reducing atmosphere with a H₂X gas, wherein X is S, Se, or Te; and

(iii) recovering the metal II-intercalated and/or metal II-encagedinorganic fullerene-like (IF) structures of the metal I chalcogenide.

The expression “inorganic fullerene-like” (“IF”) as used herein refersto inorganic metal chalcogenide structures having one layer or nestedlayers which form what is known in the art as a closed cage (Tenne etal., 1992; Margulis et al., 1993) which may encage a core or may form astuffed nested layer structure. In particular, the term refers tostructures such as what is known in the art as single and double layerinorganic fullerenes (Srolovitz et al., 1995), nested layer inorganicfullerene (Tenne et al., 1992), stuffed inorganic fullerenes (Marguliset al., 1993), structures with negative curvature (Schwartzites), singlelayer nanotubes (Bethune et al., 1993; Iijima and Ichiashi, 1993),nested nanotubes (Iijima, 1991) and stuffed nanotubes (Ajayan andIijima, 1993).

Thus, IF structures of metal I chalcogenides intercalated with metal IIparticles, said IF structures including one or more metal I chalcogenidelayers of desired size and shape (e.g. spheres, nanotubes, structureswith negative curvature (Schwartzites), and polyhedral shapes), beinghollowed or having a metal II-doped metal I oxide core, may be producedusing the method of the present invention.

As used herein, “metal II-encaged IF structures of metal I chalcogenide”refers to IF structures including 1-2 layers of the metal Ichalcogenide, e.g. sulfide, encaging a metal II-doped metal I oxidecore, and “metal II-intercalated IF structures of metal I chalcogenide”refers to IF structures including more than 2 layers of the metal Ichalcogenide, e.g. sulfide, either intercalated with metal II and beingdevoid of a metal oxide core (after full conversion of the oxide tosulfide) or being metal II-intercalated and encaging a metal II-dopedmetal I oxide core (partial conversion of the oxide).

The metal II-doped metal I oxide can be obtained in the form ofnanoparticles or nanowhiskers according to controllable change ofparameters of the reaction. Thus, for example, for the preparation of Nadoped-WO_(3−x), W is heated in the presence of water vapor bytransferring a current of about 100 Amp and about 10 volt during which aplume of metal oxide is formed within the vacuum system, and colorationof the bell-jar due to deposition of a fine powder of the metal oxide onthe walls is obtained. For the obtention of nanoparticles of Nadoped-WO_(3−x), the amount of water used is about 2-3 cc and theevaporation should not take more than 5 min, i.e. the current is stoppedat most 5 minutes counted from the moment that the deep blue plume isobserved, while for the obtention of nanowhiskers, the amount of watershould be 3-5 cc and the duration of the evaporation should be of 5-10min.

The shape of the metal II-intercalated and/or metal II-encaged IFstructures of metal I chalcogenide obtained from the metal II-dopedmetal I oxide will depend on the shape of the latter. Thus,nanoparticles of the metal oxide will produce single layer IF and nestedlayer IF, while nanowhiskers of the metal oxide will produce singlelayer and nested layer nanotubes. Thus according to the invention it wasfor the first time possible to produce metal-intercalated IF structuresof a metal chalcogenide encaging metal particles in its core, with apredetermined shape.

Thus, in another aspect, the present invention provides novel metalII-intercalated and/or metal II-encaged inorganic fullerene-like (IF)structures of a metal I chalcogenide, wherein metal I and metal II areas hereinabove defined and said structures include one or more layers ofdesired size and shape e.g. spheres, whiskers and polyhedral shapes,such as nested fillerenes and nanotubes with single, double or multiplelayers, which may encage a metal oxide core or a void (i.e. be hollowed,after full conversion of the metal oxide) and structures with negativecurvature (Schwartzites).

The new metal II-intercalated and/or metal II-encaged IF structures ofmetal I chalcogenides of the invention give stable suspensions in polarsolvents, e.g. water, alcohols, etc., i.e. they do not decompose norprecipitate as the non-metal intercalated IF structures of the priorart.

Thus, in still another aspect, the invention provides a method for theproduction of thin films of metal II-intercalated and/or metalII-encaged IF of metal I chalcogenides, which method comprisessuspension of said metal Il-intercalated and/or metal II-encaged IF in apolar solvent and either evaporation of the solvent or electrophoreticdeposition onto a conductive, e.g. gold, substrate. These thin films,most preferably films obtained from metal II-encaged IF structures ofmetal I chalcogenide as defined herein, can be used as thephotosensitive element in solar cells, in electrochromic devices, inbatteries such as Li rechargeable , hydride and rechargeable batteries,and for coating SPM tips.

Thus, in a further aspect, the invention relates to tips for scanningprobe microscopy (both STM and SFM) such as Si or Si₃N₄ tips, which arecoated with a single layer of a metal II-encaged or metalII-intercalated IF of a metal I chalcogenide. These IF-coated tips arerobust and show low adhesion, and are prepared by depositing films ofthe IF structures on the tips.

In still another aspect, the present invention relates to the use of themetal II-intercalated and/or metal II-encaged inorganic IF structures ofa metal I chalcogenide of the invention as lubricants, particularly insolid lubrication, such as in high or low temperature environments orunder ultra high vacuum where liquid lubricants are not suitable (seeDimigen et al., 1979) and in ferrofluid lubrication, sealing andlevitation applications. Since the outer surface of the IF materialexposes only the basal plane of the compound, this material lends itselfto solid lubrication applications. Indeed, IF nanoparticles do not stickto each other or the substrate and exhibit poor surface adhesion. Theirapproximate spherosymetric shapes imply easy sliding and rolling of thenanoparticles and consequently very small shear forces are required tomove them on the substrate surface.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a flow chart of the processes used for synthesizingalkali-metal intercalated IF structures and for fabricating the films,from, e.g. IF-WS₂ (MoS₂). To obtain the suspensions, a 50 mg portion ofIF particles (nanotubes) was mixed with 50 ml ethanol, and the mixturewas sonicated for 5 min.

FIG. 2(a) is a schematic representation of the evaporation apparatusused for the synthesis of the oxide nanoparticles and whiskers. In thefirst stage, the belljar was evacuated to ca. 10⁻⁵ Torr. The tungsten(molybdenum) wire was cleaned by heating it close to its meltingtemperature for a few minutes, after which the system was allowed tocool to ambient temperatures. The bell-ar was opened for a short whileand a beaker with about 3 ml of water was inserted. Upon evacuation toabout 10⁻³ Torr, the water in the beaker froze. At this point the gatevalve was closed and the W wire heated again. After a few minutes thewall of the belljar was covered with a blue oxide powder which wascollected for characterization and further processing. The size of theoxide particles and their shape could be varied according to the processparameters, like pumping speed, vacuum, etc. FIGS. 2b-2 d are TEM imagesof the oxide precursors: 2(b) small (<10 nm) and 2(c) large (ca. 50 nm)spherical particles; 2(d) whiskers.

FIGS. 3a-3 d are TEM images of tungsten-sulfide nanoparticles obtainedfrom the oxide precursors shown in FIG. 2: 3(a) oblate andquasi-spherical IF particles; 3(b) nanotubes; 3(c) torus exhibitingnegative curvature (Schwartzite). FIG. 3d shows a full-fledged IF-WS₂film on a Au substrate. The IF film was deposited by first evaporating agold film (35 nm) on mica and annealing it to 250° C. for 12 hr, whichresulted in {111} textured Au crystallites with a typical size of 1 mm.The IF films were obtained by applying a bias of 20 V between the goldcathode and a Pt foil which were immersed in the intercalated IFsuspension. IF films up to 500 nn in thickness were obtained by thisprocedure.

FIG. 4 is a TEM micrograph showing the lattice image of VS₂ nestedfullerene-like particles obtained from the respective oxidenanoparticles which were produced by the apparatus of FIG. 2a. Latticespacing (c) is 0.61 nm.

FIG. 5, curve (a), shows powder diffraction of IF-WS₂ with sodium asintercalant; and curve (b) shows WS₂ platelets (the peak at 13° isassigned to the CuK_(β)).To preclude parasitic scattering, the specimenswere deposited on background-free single crystal quartz plates. Stepsize was 0.005° and exposure time was 6 s/point. The square rootintensity presentation was used to increase the dynamic range of thefigure.

FIG. 6 shows photoresponse spectra of thin films of IF-WS₂: (a) IF filmwith low density of dislocations; (b) film consisting of IF particleswith a high density of dislocations; and (c) nanotubes. The insetpresents EET spectra of: (a) dislocation-free IF film and (b) nanotubes.The EET spectra were obtained by measuring the transmission spectrumwhile superimposing an ac modulation of 0.45 V on the photoelectrode.

FIG. 7 shows scanning tunneling current spectroscopy of fullerene-likeWS₂ films deposited on a gold substrate, using a Pt-Ir tip. Curve a isan I-V plot showing a bandgap of about 1.6 eV; curve b shows backgroundac signal without illumination; and curve c- shows an I-V plot undermodulated 650 nm illumination, attenuated by a factor of 4. Themodulation signal represents the lock-in output in arbitrary units,whereas the I-V signal is in nA. The peaks at negative sample bias incurves b and c are an artifact due to capacitive pickup. Prior to themeasurements, the sample was wetted with selenosulfate solution, andthen dried for about 30 min. Inset: topography taken with a sample biasof 50 mV; a current setpoint of 0.7 nA, under cw laser illumination (650nm), showing a group of fullerene-like structures on a gold terrace. Theillumination induces strong tunneling current over the IF, allowing itto be seen as protrusions on the surface (contrast to curve a).

FIG. 8 shows contact-mode SFM image of the IF-WS₂ film used in theexperiments of FIG. 5, obtained with the Si/IF composite tip, which wasprepared by electrophoretic deposition of IF film on the Si tip. Toprepare the IF coated tip, the Si cantilever was inserted into the IFsuspension with an average particle size of 30 nm. A Pt foil served asanode, and a bias of 20 V was applied between the cathode and anode forca. 1 min.

FIG. 9 shows TEM image of IF-SnS₂ nanoparticles obtained by the processof the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention will now be illustrated in a non-limiting way according tothe following examples and the accompanying drawings.

EXAMPLE 1

General procedure for synthesizing alkali-metal intercalated IFstructures and for fabricating the films: As illustrated in the flowchart of FIG. 1, the processes used for synthesizing alkali-metalintercalated IF structures and for fabricating the films. from, e.g.IF-WS₂, comprise the following steps.

The first step in this hierarchy consists of synthesizing oxide powderin a modified vacuum deposition apparatus (see FIG. 2a). For thatpurpose, a W (or other metal) wire was heated and evaporated in thepresence of water vapor. Metal or metal oxides could be evaporated fromtungsten boats, but this would usually lead to mixed tungsten-metaloxide (and sulfide after sulfidization) nanoparticles. To intercalatethe IF particles with metal atoms, metal-doped oxide nanoparticles werefirst prepared. This was done by dissolving 10⁻³-10⁻² M of alkali metalsalts, like NaCl, KCl, and CsCl, in the water and coevaporating ittogether with the heated wire to form alkali-doped metal oxides. Furtherexperimental details of the apparatus and the work protocol aredescribed in the description of FIG. 2. As a result of this process, ablue metal oxide film accrued on the walls ofthe bell-jar.

In another embodiment of this first step, electron beam evaporation of ametal I material is carried out with water or with an oxygen-containingvolatile solvent in a vacuum apparatus at a base pressure of 10⁻⁵ to10⁻⁶ Torr,

In the second step of the scheme of FIG. 1, the oxide powder wasconverted into a sulfide with nested fullerene or nanotubes structures(generically known as inorganic fullerene-like material-IF), byannealing the oxide in a reducing atmosphere with H₂S gas (Feldman etal., 1996).

Stable alcoholic suspensions of the IF particles synthesized in thesecond step were obtained by mixing a few milligrams of the intercalatedIF powder in 3 ml of various alcohols, e.g. ethanol and sonication ofthe mixture (third step of scheme of FIG. 1). The solubility of the IFparticles was found to be proportional to the amount of intercalant,whereas IF particles containing >8% of alkali-metal atoms were totallystable, and nonintercalated IF particles did not form stable suspensionsat all.

Next, deposition of intercalated IF films from the suspensions wasaccomplished (fourth step in scheme of FIG. 1), using two alternativeroutes: solvent evaporation or electrophoretic deposition onto goldsubstrates, which were prepared as described (Golan et al., 1992;Alperson et al., 1995). In general, electrophoretic deposition resultedin more adhesive films and was therefore preferentially used accordingto the invention.

Transmission electron microscopy (TEM) was used for lattice imaging andelectron diffraction of the nanoparticles. The composition of the oxideand sulfide nanoparticles was established using energy-dispersive X-rayanalysis (EDS Link model ISIS) mounted on a high resolution TEM (200 kV,JEOL Model 2010) with probe size of 5 nm. The alkali metal concentrationin the oxide precursor was determined by inductive coupled plasma(Spectro- Spectroflame ICP) analysis and by X-ray photoelectronspectroscopy (Kratos Axis-HS using monochromatized Al k_(α) radiation).X-ray powder diffraction (Scintag Theta-Theta XRD equipped with liquidnitrogen cooled Ge solid state detector, equipped with Cu k_(α) anode)was used to determine the crystallinity and phase of the oxide(sulfide).

Scanning force microscope (SFM) and scanning tunneling microscope (STM)were used to image the IF film surface both in noncontact and contactmodes (SFM) and in photoassisted imaging mode (STM). All SFM and STMwork was done on a Topometrix TMX 2010 Discoverer system. For contactmode force microscopy, the probes were either Si₃N₄ (Park Scientific) orsingle crystal Si (Nanoprobe) microfabricated tips. Fullerene tips wereprepared by electrophoretic deposition on the latter, as describedbelow. For intermittent contact mode, Si probes (Nanoprobe) withresonance frequency of 260-320 kHz were used. STM was performed usingmechanically cut PtIr tips. For the photoassisted measurements, a 650nrm laser diode (Toshiba) was focused to the junction so that thefocused fluence was 30-50 mW/cm². The laser was operated either CW ormodulated at 3-5 kHz. In the latter case, the modulated current signalwas processed by a lock-in amplifier (SRS530).

Photocurrent measurements and electrolyte electrotransmission (EET) werecarried out on a standard computerized photoresponse set-up, equippedwith a light source, monochromator, potentiostat, lock-in amplifier,voltage modulator, and optics. For these measurements, a copper wire wasattached to the gold substrate of the IF film, and the entire electrode,except for the front surface, was covered with an insulating resin. Astandard photoelectrochemical cell with Pt mesh as counter electrode andPt wire as a reference electrode was used.

EXAMPLE 2

Using the evaporation method described in Example 1 above, the particlesizes (which vary between 7-50 nm) and shapes could be varied by varyingthe experimental conditions. This is illustrated by the TEM images ofthe oxide nanoparticles, as shown in FIGS. 2b and 2 c. Their compositionwas established using energy-dispersive X-ray analysis (EDS) mounted ona high resolution TEM (200 kV) and was found to vary between WO_(2.9)and WO_(2.5). Tungsten oxide is known to have stable unstoichiometricphases with O/W ratio varying in this range (Wells, 1962). The alkalimetal content in the oxide precursor was determined by inductive coupledplasma (ICP) analysis and by X-ray photoelectron spectroscopy (XPS) andwas found to vary between 4 and 8 atomic %. X-ray powder diffraction(XRD)_indicated that the oxide precursor was mainly amorphous. Using alower vacuum (10⁻³ Torr) and higher pumping speed, which produced morewater vapor, a blue powder consisting mainly of oxide nanowhiskers withan average size of 300 nm was deposited on the bell-jar (FIG. 2d).Careful control of the evaporation conditions was imperative formaintaining a high yield of the oxide nanoparticles and nanowhiskers. Inparticular, the metal cleaning process prior to the evaporation wasfound to be very important for the success of the process.

EXAMPLE 3

The sulfidization process of oxide nanoparticles and the production ofIF materials of various kinds have been developed by the presentinventors (Feldman et al., 1995, 1996). The sulfidization starts at theoutermost surface of the oxide, and the oxide core is progressivelyconsumed and converted into sulfide. For the IF-WS₂ material, asolid-gas reaction between W0₃ and H₂S has been adopted, while gas phasereaction between MoO₃ and H₂S was undertaken for the synthesis ofIF-MoS₂. Interestingly, the alkali-metal doped molybdenum-oxide powderobtained in the apparatus of the present invention (FIG. 2a) is muchless volatile than the nonintercalated nanoparticles described before.Therefore, the simpler solid-gas reaction between MoO₃ powder and H₂Sgas was adopted for the synthesis of IF-MoS₂.

Following the sulfidization of the oxide nanoparticles, IF structureswith a near to spherical shape or polyhedral topology were obtained fromthe quasi-spherical oxide particles (FIG. 3a), while nanotubes, whichwere closed at both ends, were obtained from oxide whiskers (FIG. 3b).The size of the IF particles retained the size of the oxide precursorparticles. An abundance of T-bars, closed from three ends, and in onecase even a torus (FIG. 3c) structure, all showing negative curvature(Ijima et al., 1992; Terrones et al., 1995; Dunlap, 1992), were obtainedby a similar procedure. The number of closed sulfide layers in the IFstructures could be controlled through the firing time. Because thereaction can be interrupted at any time, macroscopic amounts offullerene-like structures and nanotubes with different numbers ofsulfide layers and an oxide core including single, double, or multiplelayers (with oxide core) or fully converted (hollow) IF, were obtained.

In general, the intercalation process is not limited to the metallicatoms and intercalation of solvent molecules from solutions cannot beavoided (Somoano et al.,1979). However, in the present process, watermolecules, if at all incorporated into the oxide particles, would beoutgassed during the sulfide synthesis. Indeed, no evidence for theintercalation of solvent molecules into the host lattice was found.Furthermore, since no prismatic edge planes (1120) exist in these closedstructures, intercalation of solvent molecules, which makes the 2Hplatelets susceptible to solvent intercalation and exfoliation (Somoanoet al., 1979; Jonson et al., 1986), was avoided.

EXAMPLE 4

The above method is rather versatile and is not limited to IF of Mo or Wchalcogenides. FIG. 4 presents the lattice-image of VS₂ fullerene-likeparticles which were obtained with the same apparatus. IF structures ofγ-In₂S₃ were also obtained but are not shown. The starting material forIF-VS₂ was V₂O₅ which was heated in a molybdenum boat in the presence ofwater vapor. This explains the observation that some of thenanoparticles were mixed IF-V_(x)Mo_(1−x)s₂. The precursor for In₂O₃ wasIn shot heated in a Mo boat. This shows the versatility of the presentprocedure, which in fact can be used for the synthesis of IF structuresfrom virtually any metal chalcogenide having a layered-type structure.Therefore, mixed IF of the formulas M_(1x)M_(1′1-x)S₂ andM₁S_(2-x)Se_(x) can be obtained in the process.

EXAMPLE 5

The IF powder synthesized in the second step formed very stablesuspensions in various alcohols upon sonication (third step of scheme ofFIG. 1). A picture of several vials containing suspensions of oxide(translucent blue, vial a) and IF particles (green, brown toblack-tinted, vials b, c, d) is included in FIG. 1. IF-MS₂ powders,which were synthesized according to previously reported procedures(Feldman et al., 1995, 1996), did not form stable suspensions even afterprolonged sonication. These results indicate that the intercalation ofalkali metal atoms in the van der Waals gap of the IF particles led to apartial charge transfer to the host lattice which increased thepolarizability of the nanostructures, enabling them to disperse in polarsolvents. The transparency of the suspensions and their stabilityincreased with the amount of alkali metal intercalated into the IFstructures. Suspensions prepared from IF powder (both fullerene-likeparticles and nanotubes) which contained large amount of intercalant(>5%) were found to be virtually indefinitely stable. The opticalabsorption of the IF suspensions was very similar to that of thin filmsof the same nanoparticles.

EXAMPLE 6

In the next step, films were deposited on a gold substrate byelectrophoretic deposition. Given the chemical affinity of sulfur togold, it is not surprising that electrophoretic deposition led torelatively well-adhering IF films.

Furthermore, some selectivity with respect to the IF sizes and number ofMS₂ layers in the films was achieved by varying the potential of theelectrode. The thickness of the film was controlled by varying theelectrophoresis time. FIG. 3d presents a TEM image of a very thin film(tens of nm) of IF particles together with the gold substrate. Since thenonintercalated IF particles do not form stable suspensions, films ofsuch material were obtained by electrophoresis from vigorously sonicateddispersions of the IF powder.

EXAMPLE 7

Using X-ray photoelectron spectroscopy (XPS) analysis, the alkalicontent of the IF particles was found to vary from 4-10 atom %,depending on the parameters of preparation of the oxide precursor andthe subsequent sulfidization process. X-ray diffraction patterns ofIF-WS₂ and 2H-WS₂ powders were measured using CuKa radiation (FIG. 5).The most pronounced evidence for the formation of fullerene-likeparticles is the shift of the (0002) Bragg diffraction peak toward lowerangles and the simultaneous broadening of this peak. The shift reflectsthe strain relief mechanism associated with folding of S-W-S layers(Feldman et al., 1995, 1996). The peak broadening is due to the reduceddomain size for coherent X-ray scattering in the direction perpendicularto the basal (0001) plane. The expansion along the c-axis of the IFparticles (ca. 2-4%) may also reflect the random distribution of theintercalated atoms, at least in a subgroup of the IF particles. However,the variation between the lattice spacing (d₀₀₀₂) of the IF particles,which are doped with different alkali atoms, is small (6.35 Å for Nacompared to 6.45 Å for K). The appearance of superstructure Braggdiffraction peaks at small angles (FIG. 5) strongly indicates thepresence of an ordered IF phase with staging. The three (0001) Braggreflections allude to a sixth stage (n=6) in IF-WS₂, i.e. the two Nalayers are separated by 6 WS₂ layers. The repeat distance between theadjacent intercalated layers varies from 36.7 Å for Na to 38.9 Å with K.These results suggest that two populations of fullerene-like particlesexist, one having ordered dopant atoms (staging) with n=6, the otherwith randomly distributed alkali atoms. Since the number of MS₂ layersin the IF particles varies from about 4 to 10, those particles withfewer than 6 layers cannot exhibit staging, and consequently a randomdistribution of the alkali metal atoms is thermodynamically favored inthis case. It was reported (Somoano et al., 1973) that intercalation ofalkali metal atoms into the lattice of 2H-MoS₂ did not lead to stagingand, furthermore, the intercalated material was found to be extremelysensitive to air and moisture. Finally, two additional weak diffractionpeaks with lattice spacing of 2.81 and 3.03 Å were observed. These peakswere assigned to a microphase of NaNO3, which might be formed throughthe reaction of forming gas (N₂ -95%/H₂ -5%) with oxygen duringsulfidization of the oxides.

EXAMPLE 8

The optical absorption spectra of intercalated 2H-MoS₂ did not showappreciable changes for alkali metal concentrations less than 30%, wherea transition into a metallic phase at room temperature and a furthertransition into a superconductor at about 3-7 K were reported (Brec andRouxel, 1986; Somoano et al.,1979). Since the concentration of theintercalating metal atoms did not exceed 10% here, no changes in theoptical transmission spectra were anticipated nor were found to occur.The intercalation of alkali atoms in the IF particles also inducesn-type conductivity of the host.

EXAMPLE 9

The prevalence of dangling bonds on the prismatic faces of 2H—WS₂crystallites leads to rapid recombination of photo excited carriers.Consequently, the performance of thin film photovoltaic devices oflayered compounds has been disappointing. The absence of dangling bondsin IF material suggested to us that this problem could be alleviatedhere. Therefore the photocurrent response of IF-WS₂ films inselenosulfate solutions was examined and compared to that of 2H-WS₂films. The response was found to be very sensitive to the density ofdislocations in the film. Curve a of FIG. 6 shows the quantum efficiency(number of collected charges/number of incident photons) of a typicalnested fullerene (WS₂) film with a low density of dislocations, as afunction of the excitation wavelength. On the other hand, films havingnested fullerene-like particles with substantial amounts of dislocationsexhibited a poor photoresponse and substantial losses at shortwavelengths (curve b), which indicate that the dislocations impair thelifetime of excited carriers in the film. Films of nanotubes also showedsubstantial photoresponse (curve c). Finally, films made of 2H-WS₂platelets (each about 1 mm in size), which are known to have manyrecombination centers on the prismatic edges (1120), did not exhibit anymeasurable photoresponse under comparable conditions. The photocurrentdecreased with negative bias, reaching zero at −1.0 v vs. the Pt foilcounterelectrode, thus affirming that the intercalated IF particles weren-type. The photoresponse of the IF films did not show any degradationafter 48 hr of continuous illumination. Electrolyte electrotransmission(EET) spectra of the IF films were also recorded (Bordas, 1976). Theinset of FIG. 6 shows such a spectrum, which clearly reveals the directexcitonic transitions of the film at 2.02 (A exciton) and 2.4 eV (Bexciton), respectively.

EXAMPLE 10

STM was used to probe the photoresponse of individual IF particleselectrodeposited on a gold film. Initially, STM measurements were madein the dark. Both INV spectroscopy and topographic images were made. TheI/V spectroscopy yielded either ohmic behavior (not shown) correspondingto exposed gold regions on the surface or a currentless region centeredaround 0 V bias corresponding to the “bandgap” of the individual IFparticle (curve a of FIG. 7). These data must be interpreted in theframework of a metal—semiconductor—metal structure. The log of thecurrent increases linearly with voltage, behavior which is associatedwith Poole conduction (Geddes et al., 1990). The slight currentenhancement in the positive sample bias region is expected for then-type IF under the experiment. The I/V curve could be used to determinetunneling conditions which do not sweep the IF particles away by thetip: the bias was set to 1.5 V with current setpoint <1 nA.Photoresponse was then measured by illuminating the junction withmodulated 650 nm light. The laser was applied after observing no photoeffect when using 0.5 W, mildly focused with light. Using the lock-inoutput as a measure of the photoresponse, two effects can be observed bycomparing curves b and c of FIG. 7. First, the signal level is raisedover the entire voltage scan. Secondly, significant enhancement of thesignal was observed at positive sample bias. Note that curve c in FIG. 7was attenuated by a factor of 4 to keep it on scale. The peak atnegative bias seen in both curves is an artifact due to capacitativepickup.

The current enhancement under illumination was exploited to improve theSTM imaging of the individual fullerene-like particles. Using a biasvoltage of 50 mV, conditions which would not allow observation of thefullerene-like particles in the dark, the sample was imaged under CWillumination. The resulting image is shown in the inset of FIG. 7. Thecontrast between the IF particles and the gold substrate stems from thephotosensitivity of the former, which produced large current contrasteven under small bias. This effect also indicates that the response isdue to photocurrent, not photovoltage, which would have a much smallercurrent dependence on distance. Choice of small bias sets thetip-surface distance and hence impedance to a relatively low value,which increases sensitivity to the photocurrent. The photoassisted STMimaging was obtained only after the film was wetted by a drop of aselenosulfate solution.

The effect of the tip proximity in the STM experiments must also beconsidered: tip-induced band-bending due to a surface space-chargeregion can lead to a reduced current for the lower bias values. Althoughthe Na concentration is high enough to lead to a very small space-chargeregion if there was full charge transfer from the alkali metal atoms tothe host, the actual charge transfer is only partial.

EXAMPLE 11

The photocurrent observed in the IF film can be explained by separationof photogenerated charges by a space charge layer in the semiconductor,which however is not likely to be very large in these nanostructures. Asecond possible explanation may be that the photocurrent flow isdetermined by preferential trapping/transfer of either photogeneratedelectrons or holes. In this scenario, the free charge defines theposition of the Fermi level upon illumination. Photosensitive films ofthis kind can be used for various purposes, including thephotoremediation of water, photochemical storage of solar energy, etc.The d-d nature of the photoexcitation process prohibits degradation ofthe film photoresponse over extended periods of time (24).

We found that the relatively low affinity of the IF to any surface madetheir imaging with scanning force microscopy-SFM, problematic. Usingcontact-mode SFM with Si or Si₃N₄ cantilever/tip, the fullerene-likeparticles were brushed aside and the images were blurry andirreproducible. This was true both at ambient and low humidityconditions, and using cantilevers with lateral (torsional) springconstants of 3-250 N/m, with the lowest workable loading force,typically 5-20 N/m. Using the noncontact mode, the IF were clearly seen,which proves that this imaging problem is related to the affinitybetween the tip and surface. To reduce the interaction between the tipand the IF, thin layer of IF-WS₂ particles was deposited from thealcoholic suspension, using the Si cantilever/tip as a cathode. Withthis new tip, clear images of the IF film surface were obtained incontact mode (FIG. 8). This “IF-tip” was extremely robust, and was usedto image several surfaces at high and low forces without degradation.The reason for the stability of this composite Si/IF tip compared toevaporated or electrodeposited IF film, has yet to be determined.Presumably, the stability of this composite tip is related to thepresence of a high electric field because of the sharp tip, which makesa more stable bond between the IF particle and the Si tip. By imaging aNb thin film surface with sharp features (General Microdevices), weestimate this tip radius to be 20 nm, which coincides with a typicallysized IF particle. This new composite tip is now being considered forSFM-imaging of various objects.

EXAMPLE 12

Tungsten wire (0.5 mm) was connected to Cu electrodes within a bell-jarwhich were connected to a power supply outside the bell-jar. In order toclean the wire, the belljar was evacuated to 10⁻⁵ Torr and the tungstenwire was heated close to its melting point for a few minutes. The wirewas cooled down to ambient temperature and the bell jar was opened. 6 mgof NaCl were dissolved in 1 liter of ultrapure water, which produced amother solution of 10-⁴M with respect to the salt. Salts of other alkalimetals or transition metals were also dissolved in concentrationsranging between 10⁻⁴ to 10⁻³ M and then codeposited to give metal-dopedoxide powder with particles of about 30-50 nm in diameter. Higherconcentrations of the metal salt were also used but produced fullerenesof poorer quality and morphology, after annealing in H₂S atmosphere. Ifno metal was dissolved in the water, the metal containment in theresulting oxide depended on the purity of the source water. At thispoint, a beaker containing 3-5 ml of water was put in the bell-jar closeto the wire. The bell-jar was evacuated again until the water becamefrozen and the vacuum reached about 10⁻³ Torr. At this stage the vacuumpump was turned-off (gate shuttered); the power supply was turned-on andthe tungsten wire was heated to a red color. The process was continuedand deep blue-purple powder accrued on the walls of the bell-jar. Thepower-supply was turned-off when the current started to fluctuate (5-7min). The bell-jar was cooled down and the powder was collected from thewalls. The oxide powder was examined by a number of techniques.Transmission electron microscopy (TEM) and electron diffraction (ED)were used to examine the size distribution of the nanoparticles and thedegree of crystallinity. In addition, powder x-ray diffraction (XRD) wasused to identify the phases and the average crystallinity of the powder.The typical size of the particles was 50-60 nm as shown in FIG. 2c andthey were mostly amorphous. XPS revealed that the powder consisted ofsuboxide of the average formula WO_(2.8). XPS was also used to estimatethe amount of alkali metal (Na) in the oxide, which was found to varyfrom 4-8 atom %.

EXAMPLE 13

This experiment was performed as described in Example 12, except for theamount of water in the bell-jar in the first step, that was around 2 ml,and the deposition time for the oxide powder, that was 4 min. In thiscase, the Na-doped tungsten oxide powder obtained exhibited a deeperblue color and the nanoparticles were of an average size of 4-5 nmn, asdetermined both by XRD and TEM measurements, and shown in FIG. 2b.

EXAMPLE 14

Whiskers of tungsten oxide were prepared by a similar procedure to theprevious examples 12-13, except that in the second step the vacuumsystem was partially left on during the heating process of the tungstenwire. Tungsten oxide whiskers of 300 nm average length and 15 nrdiameter were obtained (shown in FIG. 2d).

EXAMPLE 15

This experiment was carried out similar to Example 14 but the saltsadded to the water were CoCl_(2.)6H₂O and FeCl₃.6H₂O (atomic ratio 1/1),in the concentration of 10⁻³ M. The average length of the Co+Fe-dopedtungsten oxide whiskers increased to 500 nm, instead of the average sizeof 300 nm in the absence of the transition metal ions.

EXAMPLE 16

A pellet of vanadium pentoxide (V₂O) was put in a tungsten boat andconnected to the Cu electrodes within the bell-jar. The rest of theprocess followed examples 12 and 13, but the first (cleaning) step wasomitted in this case. Na-doped V₂O₅ nanoparticles were obtained.

EXAMPLE 17

Indium ingot was put in the tungsten boat, heated to melting under 10⁻⁵Torr. A spherical drop of In melt was formed and the process continueduntil the sphere became shiny with a metallic luster (ca. 6 min). Thepower supply was turned down and the rest of the process followedexamples 12 and 13. Na-doped ln₂₀ ₃ nanoparticles were obtained.

EXAMPLE 18

WO_(2.8) powder with particles of average size of 60 nm (NaCl or KCldoped) was annealed in forming gas (5%H₂;95%/N₂) atmosphere and H₂S gasat 800° C. for 30 min until all the oxide was converted into tungstendisulfide (WS₂). The powder was examined, in addition to the methods ofExample 1, also by low angle X-ray diffraction technique. The particleswere shown to have fullerene-like structure (FIG. 3a) of an average sizeof about 30 nm. The XRD spectrum (FIG. 4) shows clearly a strong (0002)peak at 14.0° . Low angle diffraction peaks are a manifestation ofsodium intercalation. The diffraction strongly indicates a staging ofn=6, i.e. 6 layers of WS₂ followed by a layer of sodium. The peaks canbe translated according to the Bragg law into the following repeatdistance between intercalated metal layers: 3.67 nm for Na intercalationand 3.89 nm for K intercalation.

EXAMPLE 19

Tungsten oxide powder consisting of nanowhiskers was annealed accordingto the procedure of Example 3. FIG. 3b shows an assortment of WS₂nanotubes.

EXAMPLE 20

Sn ingot was heated in a tungsten boat to melting under 10⁻⁵ Torr. Aspherical drop of Sn melt was formed and the process continued until thesphere became shiny with a metallic luster. The power supply was turneddown and the rest of the process followed examples 12 and 13.TheNa-doped SnO₂ obtained was annealed with H₂S. FIG. 9 shows an IF-SnS₂nanoparticle obtained through this process.

EXAMPLE 21

A Nb ingot (20 g) was placed in an electron beam evaporation apparatus.The ingot was degassed at 10⁻⁶ Torr by bombardment with electron beamfor 20 min, the vacuum was broken for a very short time (<I min) and abeaker containing 15 ml of water was inserted. The vacuum was restoredand the electron beam source (tungsten wire) was actuated throughheating (20 kV; 6 mA). At this point a gray-white powder of amorphousNa-doped niobium oxide accrued on the bell-jar walls. When the processended, the oxide powder was collected, rinsed with ethanol andsubsequently analyzed by TEM; XRD, etc. Instead of water, anoxygen-containing volatile solvent such as acetone or ethanol, can beused.

EXAMPLE 22

This experiment was carried out as in Example 2 with a V ingot (20 g).An olive green powder of amorphous Na-doped vanadium oxide accrued onthe bell-jar walls.

EXAMPLE 23

Applications of the doped metal oxides and of the metal-encaged metalchalcogenides.

The metal II-doped metal oxides prepared by the method of the inventionhave several applications. The basic unit block of many of thetransition metal oxides consists of a central metal atom and 6 oxygenatoms in the vertices of an octaheder. In the ReO₃ structure theoctaheders are connected through their comers, and so each oxygen isshared by two octaheders, while for the rutile structure they areconnected through edges and hence each oxygen atom is shared betweenthree octaheders. Powder of oxide nanoparticles have number of importantapplications, in ceramics, catalysis, electrochromism (photochromism)and batteries. In all these fields the size of the nanoparticles; itsstructure; chemical composition; and its surface structure, play a majorrole in its functionality.

23 (a) Photochromism and electrochromism: The ability of an oxideparticle to modify its absorption spectrum according to the oxidationstate of the central metal atom can be utilized, e.g. for control of thetransmissivity of windows (windshields) according to the hour of the dayor the intensity of the lights of the coming car (smart windows) (see S.K. Deb, J. Chem. Phys., 37, 4818 (1966); Philos. Mag., 27, 807 (1973)).Application in information storage is also potentially very important(see R. J. Colton, A. M. Guzman and J. W. Rabalais, Acc. Chem. Res., 11,170 (1978), however crystalline oxide films suffer from a majordrawback, i.e. the color change is rather slow. The speed of theinsertion reaction of M (M=H, Li, Na, K . . . ) ions was found to bemuch faster with amorphous oxide particles (see J. N. Yao, K. Hashimoto,and A. Fujishima, Nature, 355, 624 (1992).

The metal-doped metal oxide nanoparticles obtained by the presentinvention have higher conductivity than the free metal oxide particlesand hence they can exhibit color changes due to applied bias withsmaller resistive (potential) losses, which is advantageous, inparticular for large surfaces (windows, etc.). Sulfidizing the topmostsurface of the metal-doped oxide brings about a slight color change(darker color). However, it has the advantage that it preserves theparticle size and shape after many charge/discharge cycles.

For the manufacture of an electrochromic device based on a metal-encagedIF structure of WS₂, Na-doped WO₃ powder with particle sizes of theorder of 50 nm was used as the starting material. Reduction and surfacesulfidization was carried-out in H₂S—H₂/N₂ gas mixture as describedherein. Nanocrystallites consisting of 2 closed shells of IF-WS₂ andoxide core were prepared in this way. The starting material had verylight brown color at this stage. The powder was suspended in ethanol andelectrophoretically deposited onto indium-tin oxide (ITO) glass with atypical transparency of 85% and resistivity of 20 Ohms/square. A Ptplate served as counter electrode. A propylene carbonate solutioncontaining 0.3 M LiClO₄ and 0.03 M LiBF₄ was used for the cell. Scanningthe film in the cathodic direction resulted in deep blue coloration ofthe film. The color of the film was bleached upon anodic scan. Thisprocess was repeated 5 times.

23 (b) Intercalation batteries and fuel cells: Li rechargeable batteriesare based on Li ions in electrolyte solutions, which are intercalated tothe negative electrode and deintercalated from the positive electrode.Upon reversal of the potential direction, the opposite process occurs(see A. R. Armstrong and P. G. Bruce, Nature, 381, 499 (1996). Theelectrodes are therefore made of materials that canintercalate/deintercalate the Li ions. The use of various oxide hosts,like MnO₂, Mn₂O₄, V₂O₅, CoO₂, MoO₃, WO₃, and TiO₂ for insertion andintercalation in Li batteries is being intensively investigated (seeH.-K. Park, W. H. Smyrl, and M. D. Ward, J. Electrochem. Soc., 142 1068(1995)); S. Y. Huang, L. Kavan, I. Exnar, and M. Grätzel, ibid., 142,L142 (1995)). V₂O₅ is also used in the photographic industry forantistatics (prevention of charge accumulation). The application of acomposite Pt/WO₃ electrode for the oxidation of methanol and formic acidin acidic solutions, which could be used as the anode in a fuel cell,was reported. ( K. Y. Chen, P. K. Shen, and A. C. C. Tsueng, JElectrochem. Soc., 142, L54 (1995).

Many of the currently investigated Li rechargeable batteries use eitheroxides or sulfides as electrode materials. The use of a metal-doped,e.g. Li-doped, V₂O₅ nanoparticles encaged by 1-2 layers of vanadiumdisulfide VS₂ has the advantage that the sulfide layer preserves theintegrity of the oxide nanoparticles for many charge/discharge cycleswithout influencing too much the diffusivity of the Li into the oxide orits out diffusion from the oxide nanoparticle.

For a Li rechargeable battery, Li-doped V₂O₅ powder consisting ofparticles of average diameter of 100 nmm was prepared according to theprocedure described in Examples 12 and 13. Annealing of this powder (1min) under H₂S/forming gas atmosphere at 830° C. lead to the formationof 1-2 complete monolayers of vanadium disulfide on the outercircumference of the oxide nanoparticle. Thus a powder consisting ofnanocrystallites with vanadium oxide core and thin vanadium disulfideshell was obtained. The powder was mixed with polymer binder and spancoated on Ti substrate. Subsequently, the specimen was dried in 60° C.This specimen served as cathode in the battery. For the anode, Li—Alalloy was used. Ethylene carbonate-propylene carbonate electrolyte wasused in the cell. Polypropylene foil was used as separator. Thetheoretical open circuit voltage of the cell is 3.2 V. The initialvoltage of the cell was measured to be 2.95 V. The cell was dischargedfor 10 hours at 1 mA/cm². During this period of time the voltage droppedfrom 2.9 to 2.5 V.

For a hydride battery, Na-doped WO3 powder consisting of particles ofaverage diameter of 100 nm was prepared according to the proceduredescribed in Examples 12 and 13. Annealing of this powder (1 min) underH₂S/forming gas atmosphere at 830° C. lead to the formation of 1-2complete monolayers of tungsten disulfide on the outer circumference ofthe oxide nanoparticle. Thus a powder consisting of nanocrystalliteswith (reduced) oxide core and thin sulfide shell was obtained. Thepowder was mixed with polymer binder and span coated on W substrate.Subsequently, the specimen was dried in 60° C. This specimen served asanode in the battery. For the second electrode (cathode), carbon blackpowder was mixed with polymeric binder and MnO₄/MnO₂ mixture. 4M H₂SO₄solution served as an electrolyte. Ionic membrane was used to separatethe two half cells. In the present form, the cell is in the dischargedstate. The theoretical open circuit voltage of the cell is 1.65 V. Theinitial voltage of the cell was measured to be 1.6 V. The cell wasdischarged for 8 hr at 1.0 mA/cm². During this period of time thevoltage dropped from 1.65 to 1.2 V. The charge/discharge cycles wererepeated three times.

For a rechargeable battery, Co-doped WO₃ powder consisting of particlesof average diameter of 100 nm was prepared according to the proceduredescribed in Examples 12 and 13. Annealing (1 min) of this powder underH₂S/forming gas atmosphere at 830° C. lead to the formation of 1-2complete monolayers of tungsten disulfide on the outer circumference ofthe oxide nanoparticle. Thus a powder consisting of nanocrystalliteswith oxide core and thin sulfide shell was obtained. The powder wasmixed with polymer binder and span coated on Ti substrate. Subsequently,the specimen was dried in 60° C. This specimen served as anode in thebattery. For the second electrode (cathode), carbon black powder wasmixed with polymeric binder and MnO₂. 4M H₂SO₄ solution served as anelectrolyte. Ionic membrane was used to separate the two half cells. Inthe present form, the cell is in the discharged state. The theoreticalopen circuit voltage of the cell is 1.5 V. After charging in agalvanostatic mode at 2 mA/cm², the cell was discharged. The initialvoltage of the cell was measured to be 1.4 V. The cell was dischargedfor 5 hours at 1 UA/cm². During this period of time the voltage droppedfrom 1.4 to 1.1 V. This procedure was repeated 4 times.

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What is claimed is:
 1. A method for the preparation of nanoparticles ornanowhiskers of a metal II-doped metal I oxide, wherein said metal I isselected from In, Ga, Sn and a transition metal and said metal II is anymetal, which method comprises: (i) heating a metal I material with waterin a vacuum apparatus at a base pressure of 10⁻³ to 10⁻⁵ Torr orelectron beam evaporating a metal I material with water or with anoxygen-containing volatile solvent in a vacuum apparatus at a basepressure of 10⁻⁵ to 10⁻⁶ Torr, in the presence of a metal II salt;, and(ii) recovering the metal II-doped metal I oxide powder from the wallsof the vacuum apparatus.
 2. A method according to claim I wherein saidtransition metal I includes Mo, W, V, Zr, Hf, Pt, Re, Nb, Ta Ti, and Ru,and said metal II is selected from an alkali, alkaline earth or atransition metal.
 3. A method according to claim 1 wherein said metal IIsalt is an alkali metal chloride.
 4. A method according to claim 1,wherein said metal II-doped metal I oxide is a metal II-doped mixedoxide of 2 or more different metal I atoms.
 5. A method according toclaim 1 for the preparation of nanoparticles or nanowhiskers of dopedmetal oxides selected from Na—, K—, Li— or Cs-doped MoO_(3−x),preferably MoO₂ and MoO_(3,), or Na—, K—, Li— or Cs13 doped WO_(3−x),preferably WO₃ and W₁₈O₄₉ , and Na—, K—, Li— or Cs-doped mixed Mo/Woxide consisting of Mo_(x)W_(1−x)O₃, wherein x is from 0 to
 1. 6. Amethod according to claim 1, wherein said metal II salt is added to thewater or to the oxygen-containing volatile solvent.
 7. A methodaccording claim 1, wherein said metal II salt is NaCl or KCl and it isalready present in the water.
 8. A method for the preparation of metalII-intercalated and/or metal II-encaged inorganic fullerene-like (IF)structures of a metal I chalcogenide, wherein said metal I is selectedfrom In, Ga, Sn and a transition metal and said metal II is any metal,which method comprises: (i) heating a metal I material with water in avacuum apparatus at a base pressure of 10⁻³ to 10⁻⁵ Torr or electronbeam evaporating a metal I material with water or with anoxygen-containing volatile solvent in a vacuum apparatus at a basepressure of 10⁻⁵ to 10⁻⁶ Torr, in the presence of a metal II salt; (ii)aimealing the metal II-doped metal I oxide obtained in step (i) in areducing atmosphere with a H₂X gas, wherein X is S, Se, or Te; and (iii)recovering the metal II-intercalated and/or metal II-encaged inorganicfullerene-like (IF) structures of the metal I chalcogenide.
 9. A methodaccording to claim 8 wherein said metal II-intercalated and/or metalII-encaged inorganic fullerene-like structures of a metal I chalcogenideare structures having one layer or nested layers which form a closedcage which may encage a core or may form a stuffed nested layerstructure, particularly structures selected from single and double layerinorganic fullerene-like structures, nested layer inorganicfullerene-like structures, stuffed inorganic fullerene-like structures,structures with negative curvature (Schwartzites), single layernanotubes, nested nanotubes and stuffed nanotubes.
 10. A methodaccording to claim 8 wherein nanoparticles of the metal oxide obtainedin step (i) produce single layer IF and nested layer IF, andnanowhiskers of the metal oxide obtained in step (i) produce singlelayer and nested layer nanotubers.
 11. A method according to claim 8,wherein said transition metal includes Mo, W, V, Zr, Hf, Pt, Re, Nb, TaTi, and Ru, and said metal II is selected from an alkali, alkaline earthor a transition metal.
 12. Metal II-intercalated and/or metal II-encagedinorganic fullerene-like (IF) structures of a metal I chalcogenide,wherein said metal I is selected from In, Ga, Sn and a transition metaland said metal II is any metal.
 13. The metal II-encaged inorganicfullerene-like (IF) structures of a metal I chalcogenide according toclaim 12, wherein said structures include 1-2 layers of the metal Ichalcogenide encaging a core of the metal II-doped metal I oxide.
 14. Atip for scanning probe microscope coated with a single layer of a metalII-intercalated and/or metal II-encaged IF of metal I chalcogenideaccording to claim
 13. 15. The metal II-intercalated inorganicfullerene-like (IF) structures of a metal I chalcogenide according toclaim 12, wherein said structures include more than 2 layers of themetal I chalcogenide intercalated by metal II and encaging a core of themetal II-doped metal I oxide.
 16. The metal II-encaged inorganicfullerene-like (IF) structures of a metal I chalcogenide according toclaim 12, wherein said structures include more than 2 layers of themetal I chalcogenide intercalated with metal II and devoid of a core.17. Metal II-intercalated and/or metal II-encaged inorganicfullerene-like (IF) structures of a metal I chalcogenide, according toclaim 12, wherein said transition metal I includes Mo, W, V, Zr, Hf, Pt,Re, Nb, Ta Ti, and Ru, and said metal II is selected from an alkali,alkaline earth or a transition metal.
 18. Use of metal II-intercalatedand/or metal II-encaged inorganic fullerene-like (IF) structures of ametal I chalcogenide according to claim 12 as lubricant, particularly insolid lubrication.
 19. A stable suspension in a polar solvent of atleast one of a metal II-intercalated IF structure and a metal II-encagedIF structure of a metal I chalcogenide, wherein said metal I is selectedfrom the group consisting of In, Ga, Sn and a transition metal, and saidmetal II is any metal.
 20. A method for the production of thin films ofmetal II-intercalated and/or metal II-encaged IF structures of metal Ichalcogenides, which comprises subjecting a stable suspension accordingto claim 19 to evaporation of the solvent or to electrophoreticdeposition onto a conductive substrate.
 21. Use thin films of metalII-intercalated and/or metal II-encaged IF structures of metal Ichalcogenides obtained according to claim 20, as the photosensitiveelement in solar cells, for the fabrication of secondary batteries andin electrochromic devices.